Punctureproof tube and method of making same



J. W. WABER PUNTUREPROOF TUBE AND METHOD OF.' MAKING SAME Filed June 16,1934 SVT Patented Mar. 17, 193e PUNCTREPROOF TUBE AND METHOD F MAKINGSAME James W. Waber, Chicago, Ill. Application June 16, 1934, Serial No.730,878

Claims.

This invention relates to a new and useful improvement in the method orprocess of making punctureproof tubes, such as are used in the ordinarycasings or tires of automobiles and is particularly intendedas animprovement on the process disclosed in applicants Patent No. 1,808,091granted June 2, 1931.

It may be noted that the iinished product or tube of the presentinvention may be substantially identical with that disclosed in saidpatent.

In a puncture proof inner tube consisting at the tread portion of twolayers of vulcanizable rubber between which is a layer of mastic orunvulcanizable rubber, the inner vulcanizable layer at the tread portionis removed from the vulcanizing mold by a distance of at least two orthree times its thickness. As a result, in vulcanizing or curing thetube by the process disclosed in applicants patent it is necessary thatthe vulcanizing process be continued for a substantial lengt-h of timein order to cure the inner vulcanizable layer at the tread portion ofthe tube.

'I'he object of the present invention is a process by which the innervulcanizable layer at the tread portion of the tube will become cured orvulcanized in substantially the length of time requiredv to vulcanizethe portions of the tube which are in direct contact with the mold,'I'his not only has the eii'ect of very substantially shortening theperiod of vulcanization but also results in a much more uniform product.

A feature of the invention is the treatment of the inner vulcanizablelayer of the tube at the tread portion thereofnnder the mastic with asuitable vulcanization accelerator, such as Ziinate or other similarcompounds capable of accelerating or producing vulcanization of rubberat low temperatures. This accelerator is applied directly to the treadportion of the inner vulcanizable layer under the mastic and may be onthe side immediately adjacent to the. mastic or it will have the sameresult if applied on the inner surface of the said inner vulcanizablelayer.

It is believed a further disclosure of the invention will be bestunderstood from a detailed description thereof taken in connection withthe accompanying drawing in which Fig. 1 illustrates a cross-sectionthru the revolving form or working wheel with the tube of the presentinvention mounted thereon prior to its being vulcanized; and Fig. 2shows a portion of the inner vulcanizable tube formed of a strip ofrubber and the vulcanization accelerator applied to the. inner surfacethereof.

Referring now to the drawing, lll indicates the revolving form or wheelupon which the tube in process of construction may be mounted and il theaxle or support about which the wheel lli may rotate. I2 indicates theinner vulcanizable layer of the tube which may be formed of explishedthru the vtire with which the traded tubular rubber with the ends joinedtogether so as to produce an endless tube. 'This inner layer of the tubeneed not differ greatly from the ordinary automobile tire tube. VIt maybe here noted that the process preferably iollowed in the presentinvention need not differ materially from that disclosed in the abovenoted patent, except as to the use of the vulcanization accelerator. Inthe manufacture of the tubes oi' theV present invention Zimate has beenfound very satisfactory as an accelerator, although otherultra-accelerators with the same general characteristics may be usedwith vulcanizing agents and produce satisfactory results. Theaccelerator which is known under the trade-name ofnZimate consistsessentially of zinc dithiocarbonate and it isbelieved the as followsformula is (CH3) 2N.C.(S) SZnS.C.(S) BUCHS) 2.

-In carrying out this process the inner endless tube is preferablyplaced on a revolving form or wheel such as the work wheel i@ and isindimethyl-4 flated in any desired manner until it is of about thegeneral size that it will have when the tube is completed. Thisinflation may be accommedium of a valve stem which has previously beeninserted in the tube layer or may be produced thru the medium of ahollow needle inserted thru the tube wall. After the Vtube has beenplaced upon the wheel and inilated a substantially crescent shaped stripof mastic i3 is placed about the tread portion thereof, and overlyingthe mastic is placed a second vulcanizable strip it the edges of themastic and into contact with the inner layer it. In order to practicethe present invention the tread portion of the inner vulcanizable layeri2 prior to the application of the mastic thereto is treated with avulcanization accelerator i5 as indicated by the dotted portion in Fig.2.

After the tube has been built upon the wheel as just described above,`it is placed in a mold,

the inner surface of which is preferably of substantially the size andshape of the cavity in the tube is intended to be used, and vulcanizedin the usual manner.

Due to the use of the accelerator l5 it is found that the innervulcanizable layer it under the mastic will be satisfactorily cured innearly the length oi' time which is required to vulcanize the portionsof the tube which come vdirectly in contact with the mold. This greatlyshortens the time of the vulcanizing process and also gives somewhatmore reliable results.

VIn Fig. 2 is shown a method of forming the inner vulcanizable layer l2'of the tube from a strip of rubber instead of from the extruded tubesuch as described in connection with Fig. 1. In Fig. 2'the edges of thestrip are overlapped as shown at i6 and the vulcanization acceleratorl5' the edges Vof which extend beyond may be applied to the innersurface oi the tread portion of the tube instead of to the outer surfaceas shown in Fig. 1. With the exception of the manner of forming theinner vulcanizable layer of the tube the process of forming the completetube according to the structure shown in Fig. 2 may be can'ied out insubstantially the same manner as described in connection with Fig. 1.

While in the above disclosure the tube has been described as built up ona revolving form or wheel it is to be understood that the presentprocess may be carried out without resorting to 'this expedient althothis has been found to be the most satisfactory manner of forming thetube. The only requirement of the present process is that theaccelerator shall be applied to the inner vulcanizable layer of the tubeunder the mastic, either inside or outside; that the layer of mastic beapplied to the tread portion thereof and the mastic covered by an outervulcanizable layer of rubber the edges of which contact with the innervulcanizable layer and that the whole structure then be vulcanized. Itis to be understood of course that the accelerator may be applied to thetread portion of the inner vulcanizable layer in any manner or at anystage in the process so long as it is substantially confined to theportion of the inner layer which underlies the mastic.

Having thus described my invention, what I claim as vnew and desire tosecure by United States Letters Patent is:

1. An inner tube for pneumatic tires comprising a basic inner layer,annular and tubular, of

rubber lor like vulcanizable material, an outer cover layer of likematerial, both layers being fully and substantially uniformly vulcanizedor tight cured abot a layer of plastic sealing compound interposedbetween said basic layer 'and said cover layer, over the tread area,both layers of said tube being full molded throughout the arearegistering inside and out with the sealing compound in substantiallythe form and shape assumed under normal inflation, the contour of theouter layer being determined directly by the mold and that of the innerlayer being indirectly determined thereby as the sealing compoundaccommodates itself thereto and the inner layer adapts itself and theinner surface of the composition layer to the combined eiect of theshape of the mold and an internal normal inflation pressure; suchcontours being deiinitely set by the full vulcanization or "tight curingof the inner and outer layers and therefore substantially free fromstrain or distortion under normal ination, the said basic layer andcover layer being homogeneous throughout their contacting portions whenvulcanized, the portion of the basic inner layer underlying the sealingcompound having a tight cure.

2. The method of constructing an inner tube for pneumatic tirescomprising a plurality of tread layers which consists in applying to thetread portion of a vulcanizable tube a layer of plastic unvulcanizablesealing compound, covering said compound with a layer of vulcanizablematerial which extends beyond the edges of said compound and contactswith the tube for vulcanization thereto and curing all the vulcanizablematerial substantially as a whole uniformly in a mold, characterized byapplying a vulcanization accelerator to the tread part of the innerlayer; which being spaced from the vulcanization mold by the plasticunvulcanizable sealing compound would otherwise prevent or at leastdelay the vulcanization of part of the inner layer; so as to cause asubstantially uniform tight cure of both inner and outer layers withoutovercuring of any part.

3. The method of constructing an inner tube for pneumatic tirescomprising a plurality of tread layers which consists in applying to thetread portion of a vulcanizable tube a layer o! plastic unvulcanizablesealing compound, covering said compound with a layer of vulcanizablematerial which extends beyond the edges oi said compound and contactswith the tube for vulcanization thereto and curing all the vulcanizablematerial substantially as a whole in a mold, characterized by applyingprior to the unvulcanizable plastic layer, a vulcanization acceleratorto the tread part of the inner layer, which, being spaced from thevulcanizing mold by the plastic unvulcanizable material, would otherwisebe prevented from, or at least delayed in being vulcanized, so as tocause the simultaneous substantially uniform tight curing ot both innerand outer layers Without overcuring of any part.

4. Themethod of constructing an inner tube for pneumatic tirescomprising a plurality oi layers which consists in forming an endlesstube of vulcanizable material, expanding it by internal pressure,applying to the tread portion of the tube so inflated a layer of plasticunvulcanizable sealing compound and a layer of vulcanizable materialwhich extends beyond the edges of the compound and contacts with thetube for vulcanization thereto and curing all the vulcanizable materialsubstantially as a whole uniformly, characterized by applying avulcanization accelerator to the tread part of the inner layer, thespacing of which from the vulcanizing mold by the plastic unvulcanizablecompound would otherwise prevent or at least delay the vulcanization ofthis part of the inner layer, so as to cause a substantially uniformtight cure of both inner and outer layers without overcuring of anypart.

5. The method of constructing an inner tube for pneumatic tirescomprising a plurality of tread layers which consists in forming anendless tube of vulcanizable material, expanding it by internalpressure, applying to the tread portion of the tube so inated a layer ofplastic unvulcanizable sealing compound and a layer of vulcanizablematerial which extends beyond the edges of the compound and contactswith the tube for vulcanization thereto and curing all the vulcanizablematerial simultaneously substantially uniformly as a whole,characterized by applying, prior to the unvulcanizable plastic compound,a vulcanization accelerator to the tread part of the inner layer thespacing of which from the vulcanizing mold by the plastic unvulcanizablesealing compound would otherwise prevent or at least delay thevulcanization of this part of the inner layer so as to cause asubstantially uniform tight cure of both inner and outer layers withoutovercuring of any part.

JAMES W. WABER.

